The invention relates generally to pulse-jet cleaning of sleeve-type or tubular filter bags. Such filter bags are employed in baghouses that are part of industrial gas cleaners used, for example, to clean gaseous process streams. More particularly, the invention relates to an apparatus and method for improving the efficiency of pulse-jet cleaning.
An industrial flue gas cleaner of the sort in which the invention may be used is illustrated in FIGS. 1A and 1B. Dirty flue gas enters the installation through inlet manifold 10. The dirty gas is admitted into the various compartments 12 of the installation and flows upward through an array of sleeve-type or tubular filter bags 14, which are supported on the outside surfaces of cylindrical support cages 16. (See FIG. 2A.) The filter bags remove dust, soot, and other particulate matter from the gas as it passes through the filters. The clean gas then passes into and exits the installation via outlet manifold 18. Flow into and out of the individual baghouses is controlled by appropriate means such as inlet poppet dampers and outlet poppet dampers, as indicated in FIG. 1A.
As further illustrated in FIGS. 1A, 2A, and 2B, the filter bags are supported at their upper, open ends 20 by a tubesheet 22, which spans the entire cross section of the baghouse 12. The tubesheet 22 functions like a gasket, forming a seal around the upper ends of the filter bags and along the perimeter of the baghouse such that the baghouse is separated into distinct, upper and lower portions. Depending on the specific method of cleaning, the filter bags are arranged in either a rectangular or a circular array.
Common industry practice is to clean rectangular arrays of bags with compressed gas typically ranging in pressure from about 40 psig to about 120 psig (more or less depending on details of the specific design). A series of pulse pipes 24 extend across the baghouse, with one pulse pipe extending across each row of filter bags in the array. Each pulse pipe 24 has a series of orifices 26 extending along the bottom portion thereof, with one orifice positioned over each of the dust bags.
When compressed gas is used for cleaning, it is referred to as either xe2x80x9chigh-pressure/low-volumexe2x80x9d or xe2x80x9cintermediate-pressure/intermediate-volumexe2x80x9d cleaning, depending on the characteristic pressure. High-pressure systems generally operate at a pulse pressure on the order of 80 psig to 120 psig; intermediate-pressure systems generally operate at a pulse pressure on the order of 40 psig to 60 psig.
Circular arrays of bags, on the other hand, are cleaned by gas that is pressurized with a blower to pressures typically on the order of 10 psig to 20 psig (again, more or less depending on the specific design). Because lower pressures and larger volumes of gas are used in this form of cleaning, it is referred to as xe2x80x9clow-pressure/high-volumexe2x80x9d cleaning.
As shown in FIG. 2A, for all but low-pressure/high-volume cleaning, during normal filtering operation, gas with entrained particulate matter enters the baghouse 12 through inlet 30 at the lower end of the baghouse. The gas flows through the filter bags 14 (which are supported on the exterior surfaces of the cages 16) from the outside in, as indicated by the schematic cross-section of the filter bag at the top of FIG. 2A. Dust, soot, ash, and other particulate matter or debris accumulates on the outside surfaces of the filter bags, and the now-clean gas exits the baghouse through the clean gas exhaust 32 at the upper portion of the baghouse.
When debris accumulates to the point that pressure drop across the bags exceeds a preset limit, i.e., where flow through the baghouse is restricted (or in many instances on a regular, timed basis), the filter bags are cleaned of debris using the pulse pipes 24. Each of the pulse pipes is supplied with pressurized gas by pressure header 34. At the appropriate time, a valve 25 is actuated and pressurized gas flows into the pulse pipe. An energetic pulse of pressurized gas flows out of the pulse pipe through each of the orifices 26 and down into the interior of each of the sleeve-type filter bags in the row, as illustrated schematically by the cross-section of the filter bag at the top of FIG. 2B. The filer bag rapidly expands to its full circumference and then stops expanding suddenly. This rapid expansion and deceleration causes the xe2x80x9ccakexe2x80x9d of debris which has accumulated on the filter bag to fracture and be dislodged from the filter bag. The dislodged dust cake then falls into hopper 36 at the bottom of the baghouse, where it is collected and removed by an ash removal system (not shown). (The flow of dirty gas into the compartment may be suspended during cleaning of the filter bags such that the dislodged dust and other debris settles into the hopper, rather than being blown up toward the tops of the filter bags.)
Various experiments which have been conducted by, for example, Southern Research Institute, the assignee of this application, have shown that low-pressure/high-volume pulse-jet cleaning is generally superior to high-pressure/low-volume and intermediate-pressure/intermediate-volume pulse-jet cleaning. In low-pressure/high-volume pulse-jet cleaning, a blower is used to supply only moderately compressed air for the cleaning, in contrast to a high-pressure or intermediate-pressure header as shown in FIGS. 1, 2A, and 2B. Because a blower is required to supply the relatively large volume of air utilized in this form of cleaning, it generally has been conceded by those skilled in the art that multiple blowers would be required in order to apply this type of cleaning to filter bags arranged in the more conventional square or rectangular array, as they are arranged in high-pressure/low-volume and intermediate-pressure/intermediate-volume pulse-jet cleaning systems.
Providing multiple blowers, however, is not economical. Accordingly, low-pressure/high-volume pulse-jet cleaning has only been able to be realized on a commercial, practical scale by arranging the filter bags in concentric circles and supplying the pulses of air to the filter bags by means of a rotating arm. The arm rotates about an axis that is centered in the middle of the concentric circles of filter bags and is supplied with air through a central conduit, as shown, for example, in U.S. Pat. No. 4,157,899. Air is discharged into the filter bags through a series of outlets in the bottom of the rotating arm.
This arrangement is not ideal, however. In particular, it is not possible to clean every bag directly below the arm during any one pulse of air because of the manner in which the bags are geometrically distributed beneath the arm. Advocates of this arrangement point out that with multiple passes of the arm, and with pulse timing adjusted so that pulses are not directed at the same point on each rotation, statistically and over some period of time almost every bag will be pulsed. Still, however, many bags are not directly pulsedxe2x80x94i.e., a pulse of air is not directed down through the center of the bagxe2x80x94and the overall efficiency of cleaning therefore is significantly less than what it could be and what would be desired.
The present invention improves the efficiency of pulse-jet cleaning in general. Perhaps most advantageously, it eliminates the requirement of circular symmetry and rotating arms for low-pressure/high-volume pulse-jet cleaning, thereby making the superior cleaning performance of low-pressure/high-volume pulse-jet cleaning available for use in more conventional baghouse arrangements in which the filter bags are arranged in rectangular arrays. Pre-existing high-pressure/low-volume and intermediate-pressure/intermediate-volume systems could also be retrofitted to take advantage of the invention, with a concomitant reduction in the compressed air volume required for cleaning.
The invention accomplishes this by means of a novel pulse pipe in which only a few of the holes or orifices are open at any given time to permit cleaning airflow to only a subset of the filter bags in a given row at any given time. The pulse pipe remains in position over the filter bags, so every pulse is directed straight down the center of each bagxe2x80x94the most effective location for the pulse. Moreover, with only a few of the holes open for each pulse event, it becomes possible to use a relatively small, inexpensive blower to supply air to each individual pulse pipe; alternatively, a larger blower can be used to supply air to several pipes at a time using a header, valves, or suitable manifold arrangement.
In one aspect, the invention features a pulse pipe for use in pulse-jet cleaning of filter bags in a baghouse. The novel pulse pipe includes a cylindrical, hollow inner tube and a cylindrical, hollow outer tube, with the inner tube being arranged coaxially within the outer tube. The inner tube and the outer tube are configured for relative rotation therebetween about a common longitudinal axis, and the inner tube and the outer tube each have a series of longitudinally spaced apertures formed therein. The apertures in one of the tubesxe2x80x94either the inner tube or the outer tubexe2x80x94are longitudinally aligned with each other along the pulse pipe; and the apertures in the other tube are longitudinally aligned with the apertures in the first tube, but are not all longitudinally aligned with each other. As a result, different subsets of the apertures in the second tube are located at different circumferential positions on the second tube. Accordingly, as the second tube rotates relative to the first tube, different subsets of the apertures in the second tube intermittently come into alignment with the various apertures in the first tube and allow gas supplied to the interior of the inner tube to pass out of the pulse pipe.
In various embodiments of the invention, the pulse pipe may include a source of gas, and the source of gas preferably has pulse valving which regulates the supply of gas into the interior of the inner tube. Preferably, the pulse pipe also includes means for determining the relative angular position between the inner and outer tubes, and the pulse valving is regulated such that it opens to permit gas to flow into the interior of the inner tube only when apertures in the tubes are aligned.
In another aspect, the invention features a filter bag baghouse arrangement, including a chamber with a lower, inlet portion and an upper, outlet portion with a rectangular array of sleeve-type or tubular filter bags disposed therein. The filter bags are arranged in rows and columns and have closed lower ends disposed toward the inlet portion of the chamber and open upper ends disposed toward the outlet portion of the chamber. A plurality of pulse pipes as described above are disposed over the open upper ends of the filter bags, with each of the plurality of pulse pipes aligned over the filter bags in one of the rows or columns of the array. Rotation of one of the tubes relative to the other tube, as described above, causes different subsets of the apertures in the tubes to come into alignment intermittently such that gas supplied to the interior of the inner tube passes out of the pulse pipe and into a corresponding subset of the filter bags disposed below the pulse pipe in pulsed fashion.
In another aspect, the invention features a method of pulse-jet cleaning sleeve-type or tubular filter bags disposed in a rectangular array in a filter bag baghouse, which array constitutes rows and columns of filter bags. The inventive method entails intermittently injecting a low-pressure/high-volume flow of gas into varying subsets of the filter bags in each row or column in the array, with the subsets each being less than all of the filter bags in each row or column, respectively.
In preferred embodiments of the inventive method, a pulse pipe as described above is provided over each of the rows or columns in the array; gas is caused to flow into the interior of the inner tube; and gas is then injected intermittently into the varying subsets of the filter bags in each row or column by causing one of the inner and outer tubes to rotate relative to the other of the inner and outer tubes. Preferably, the pulse pipes include means for determining the relative angular position between the inner and outer tubes, and the flow of gas into the inner tube is controlled such that gas flows into the inner tube only when the tubes are oriented with the apertures therein aligned.
In another aspect of the invention, a pulse pipe for use in pulse-jet cleaning of filter bags disposed in a baghouse in a pre-determined arrangement comprises a tubular first member including a first series of apertures formed therein, a second member extending about a portion of the tubular first member and including a second series of apertures formed therein, and a source of gas configured to intermittently supply a gas pulse into an interior of the tubular first member. The first and second members are configured for movement in relation to one another such that at least some of the apertures in the second member intermittently come into alignment with at least some of the apertures in the first member and allow gas supplied to the interior of the first member to pass out of the pulse pipe.
In another aspect of the invention, a filter bag baghouse assembly comprises a chamber having an inlet portion and an outlet portion with a plurality of sleeve-type or tubular filter bags disposed therein in a pre-determined arrangement, the filter bags having closed ends disposed toward the inlet portion of the chamber and open ends disposed toward the outlet portion of the chamber, and a plurality of pulse pipes disposed near the open ends of the filter bags, wherein each of the pulse pipes comprises a tubular first member including a first series of apertures formed therein, a second member extending about a portion of the tubular first member and including a second series of apertures formed therein, and a source of gas configured to intermittently supply a gas pulse into an interior of the tubular first member. The first and second members are configured for movement in relation to one another such that at least some of the apertures in the second member intermittently come into alignment with at least some of the apertures in the first member and allow gas supplied to the interior of the first member to pass out of the pulse pipe.
In another aspect of the invention, a filter bag baghouse assembly comprises a chamber having an inlet portion and an outlet portion with a plurality of sleeve-type or tubular filter bags disposed therein in a pre-determined arrangement, the filter bags having closed ends disposed toward the inlet portion of the chamber and open ends disposed toward the outlet portion of the chamber, a first pulse pipe with a series of apertures aligned with at least a subset of the bags, and a second pulse pipe including a tubular first member including a first series of apertures formed therein, a second member extending about a portion of the tubular first member and including a second series of apertures formed therein, and a source of gas configured to intermittently supply a gas pulse into an interior of the tubular first member. The first and second members are configured for movement in relation to one another such that at least some of the apertures in the second member intermittently come into alignment with at least some of the apertures in the first member and allow gas supplied to the interior of the first member to pass out of the second pulse pipe into the first pulse pipe.
In another aspect of the invention, a method of pulse-jet cleaning sleeve-type or tubular filter bags disposed in a rectangular array in a filter bag baghouse is provided, wherein the rectangular array comprises rows and columns of filter bags, and the method comprises intermittently injecting a low pressure/high-volume flow of gas into varying subsets of the filter bags in each row or each column in the array, the subsets each comprising less than all of the filter bags in each row or each column, respectively, wherein the step of intermittently injecting a flow of gas includes supplying gas to a tubular first member with a first series of apertures formed therein and causing relative linear movement between the first member and a second member with a second series of apertures formed therein.